2013-05-03 22:25:37 +08:00
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2009-04-02 20:01:11 +08:00
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<body>
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<h1>Terminology and goals</h1>
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<p>To avoid ambiguity about the terms used, here are the definitions
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for some of the specific concepts used in libvirt documentation:</p>
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<ul>
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<li>a <strong>node</strong> is a single physical machine</li>
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<li>an <strong>hypervisor</strong> is a layer of software allowing to
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virtualize a node in a set of virtual machines with possibly different
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configurations than the node itself</li>
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<li>a <strong>domain</strong> is an instance of an operating system
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(or subsystem in the case of container virtualization) running on a
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virtualized machine provided by the hypervisor</li>
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</ul>
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<p class="image">
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<img alt="Hypervisor and domains running on a node" src="node.gif"/>
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</p>
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2011-03-28 10:40:24 +08:00
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<p>Now we can define the goal of libvirt: <b> to provide a common and
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stable layer sufficient to securely manage domains on a node, possibly
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remote</b>.</p>
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<p> As a result, libvirt should provide all APIs needed to do the
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management, such as: provision, create, modify, monitor, control, migrate
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and stop the domains - within the limits of the support of the hypervisor
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for those operations.
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Not all hypervisors provide the same operations; but if an operation is
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useful for domain management of even one specific hypervisor it is worth
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providing in libvirt.
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Multiple nodes
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may be accessed with libvirt simultaneously, but the APIs are limited to
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single node operations. Node resource operations which are needed
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for the management and provisioning of domains are also in the scope of
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the libvirt API, such as interface setup, firewall rules, storage management
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and general provisioning APIs. Libvirt will also provide the state
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monitoring APIs needed to implement management policies, obviously
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checking domain state but also exposing local node resource consumption.
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</p>
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2009-04-02 20:01:11 +08:00
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<p>This implies the following sub-goals:</p>
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<ul>
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2011-03-28 10:40:24 +08:00
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<li>All API can be carried remotely though secure APIs</li>
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<li>While most API will be generic in term of hypervisor or Host OS,
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some API may be targeted to a single virtualization environment
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as long as the semantic for the operations from a domain management
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perspective is clear</li>
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2009-04-02 20:01:11 +08:00
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<li>the API should allow to do efficiently and cleanly all the operations
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2011-03-28 10:40:24 +08:00
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needed to manage domains on a node, including resource provisioning and
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setup</li>
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2009-04-02 20:01:11 +08:00
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<li>the API will not try to provide high level virtualization policies or
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multi-nodes management features like load balancing, but the API should be
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sufficient so they can be implemented on top of libvirt</li>
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<li>stability of the API is a big concern, libvirt should isolate
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applications from the frequent changes expected at the lower level of the
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virtualization framework</li>
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<li>the node being managed may be on a different physical machine than
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the management program using libvirt, to this effect libvirt supports
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remote access, but should only do so by using secure protocols.</li>
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<li>libvirt will provide APIs to enumerate, monitor and use the resources
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available on the managed node, including CPUs, memory, storage, networking,
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and NUMA partitions.</li>
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</ul>
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<p>So libvirt is intended to be a building block for higher level
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management tools and for applications focusing on virtualization of a
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single node (the only exception being domain migration between node
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capabilities which involves more than one node).</p>
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</body>
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</html>
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